Three-dimensional graphics processing pipelines accept commands from a host (such as a central processing unit of a computing system) and process those commands to generate pixels for display on a display device. The commands may specify primitive elements (“primitives”), such as geometric shapes to be drawn. The graphics processing pipeline processes these primitives elements to generate transformed primitives elements (e.g., via a vertex shader), and then processes the transformed primitive elements (e.g., via a pixel shader) to generate pixels for output to the screen. At various stages in the graphics processing pipeline, culling operations may be performed to remove elements for which processing is not desired (e.g., because the elements would have no effect on the resulting image). In one example, primitives are culled before arrival at a pixel shader to reduce the amount of work that needs to be performed by the pixel shader. Efficiently implementing culling operations is important to operation of the graphics processing pipeline.